Devices for electrical impedance tomography (EIT) are known from the state of the art. These devices are designed and intended for generating an image, a plurality of images or a continuous sequence of images from signals obtained by means of electrical impedance measurements and data and data streams obtained therefrom. These images or sequences of images show differences in the conductivity of different tissues of the body, bones, skin, body fluids and organs, especially the lungs, which are useful for observing the situation of a patient.
U.S. Pat. No. 6,236,886 describes an electrical impedance tomograph with an array of a plurality of electrodes, power input at at least two electrodes and a method with an algorithm for image reconstruction for determining the distribution of conductivities of a body, such as bone, skin and blood vessels in a general embodiment with components for signal detection (electrodes), signal processing (amplifier, A/D converter), power input (generator, voltage/current converter, current limitation) and with components for controlling (C).
It is stated in U.S. Pat. No. 5,807,251 that it is known in the clinical application of EIT that a set of electrodes is provided, which are arranged at a defined distance from one another, for example, around the chest of a patient in electrical contact with the skin. An electric current or voltage input signal is to be applied alternatingly between different pairs of electrodes or between all the possible pairs of electrodes among electrodes arranged mutually adjacent to one another. While the input signal is applied to one of the pairs of electrodes arranged mutually adjacent to one another, the currents or voltages are measured between each pair of the other electrodes, which pairs are located adjacent to one another, and the measured data obtained are processed in the known manner in order to obtain a visualization of the distribution of the specific electric resistance over a cross section of the patient, around which the electrode ring is arranged, and to display it on a display screen.
In addition to devices for electrical impedance tomography (EIT), further medical devices suitable for imaging, for example, a great variety of radiological devices, such as X-ray apparatuses (X-ray), computed tomographs (CTs), nuclear magnetic resonance (NMR) devices, nuclear spin or magnetic resonance tomographs (MRI), as well as also sonographic devices for imaging, which make possible imaging and the providing of signals or data, as well as devices for so-called bioimpedance measurement or impedance plethysmography, are used in the area of health care. Thus, an X-ray tomography system based on gamma radiation is known from U.S. Pat. No. 4,075,482 A. U.S. Pat. No. 4,806,867 A shows a magnetic resonance imaging system. A device for improved image reconstruction of computed tomograms is described in U.S. Pat. No. 4,149,081 A. A computer-assisted system for pulmonary diagnostics, which makes it possible to identity anatomic structures of volumetric medical images, is known from U.S. Pat. No. 6,944,330 B2. A sonography device, which is suitable for an examination of the lungs and for the diagnosis especially of pulmonary diseases, especially pulmonary embolism, is known from U.S. Pat. No. 8,170,640 BB. U.S. Pat. No. 7,717,849 B2 describes a method and a device for controlling a display device in an ultrasound device, wherein selected elements of a dimensional visualization are transformed into another dimensional visualization.
Unlike imaging methods using X-ray or gamma radiation, electrical impedance tomography (EIT) has the advantage that no radiation burden that is disadvantageous for the patient occurs. Unlike sonographic methods, EIT makes possible image acquisition over a representative cross section of the entire thorax and the lungs of the patient by means of the electrode belt. In addition, the need for using a contact gel, which must be applied before each examination and thus makes a continuous sonographic examination over a longer period of time difficult, is eliminated. Thus, electrical impedance tomography (EIT) offers the advantage of making a continuous monitoring of the lungs possible in order to observe and document the course of a therapy of an artificially ventilated or spontaneously breathing patient.
It is possible by means of electrical impedance tomography (EIT) to generate so-called EIT image data for a two-dimensional image of the lungs in the plane in which the EIT electrodes are placed horizontally through the thorax of a patient. Due to the position of the EIT electrodes around the thorax, it is not possible therefore to generate frontal views or lateral views, but images are generated in the horizontal plane, the so-called transverse plane, in the EIT electrodes placed around the thorax. Additional image data can be generated for a nearly three-dimensional image of the lungs and additional views can be subsequently generated by computing in the plane of the body, such as a frontal view or sagittal view, by placing additional EIT electrodes around the thorax in different horizontal positions.
The regional distribution of the breathing air in the lungs of a patient can be considered by means of the EIT image data of electrical impedance tomography (EIT). The availability of an individually available thoracic dimension of the lungs within the individual thorax of the patient in question is of great advantage for the assessment of the current status of an artificially ventilated or spontaneously breathing patient.